Conventional batteries have been manufactured as either a wound cell battery that has only two electrodes or a standard prismatic cell battery that has many plate sets in parallel. In both of these types, the electrolyte may be shared everywhere within the battery. The wound cell and prismatic cell structures suffer from high electrical resistances due to their electrical paths having to cross multiple connections and span significantly long distances to cover the complete circuit from one cell to the next in a series arrangement.
Recently, various types of batteries with sealed cells in a stacked formation have been developed that are able to provide higher discharge rates and higher voltage potentials between external connectors than that of standard wound or prismatic batteries, and are therefore in high demand for certain applications. Certain types of these batteries with sealed cells in a stacked formation have been developed to generally include a stack of independently sealed pairs of mono-polar electrode units (MPUs). Each of these MPUs may be provided with either a positive active material electrode layer or a negative active material electrode layer coated on a first side of a current collector (see, e.g., Klein, U.S. Pat. No. 5,393,617, issued Feb. 28, 1995, which is hereby incorporated by reference herein in its entirety). An MPU with a positive active material electrode layer (i.e., a positive MPU) and an MPU with a negative active material electrode layer (i.e., a negative MPU) may have an electrolyte layer therebetween for electrically isolating the current collectors of those two MPUs. The current collectors of this pair of positive and negative MPUs, along with the active material electrode layers and electrolyte therebetween, may be sealed as a single cell or cell segment. A battery that includes a stack of such cells, each having a positive MPU and a negative MPU, shall be referred to herein as a “stacked mono-polar” battery.
The side of the current collector of the positive MPU not coated with an electrode layer in a first cell may be electrically coupled to the side of the current collector of the negative MPU not coated with an electrode layer in a second cell, such that the first and second cells are in a stacked formation. The series configuration of these cell segments in a stack may cause the voltage potential to be different between current collectors. However, if the current collectors of a particular cell contact each other or if the common electrolyte of the two MPUs in a particular cell is shared with any additional MPU in the stack, the voltage and energy of the battery would fade (i.e., discharge) quickly to zero. Therefore, it is desirable for a stacked mono-polar battery to independently seal the electrolyte of each of its cells from each of its other cells.
Other types of these batteries with sealed cells in a stacked formation have been developed to generally include a series of stacked bi-polar electrode units (BPUs). Each of these BPUs may be provided with a positive active material electrode layer and a negative active material electrode layer coated on opposite sides of a current collector. Any two BPUs may be stacked on top of one another with an electrolyte layer provided between the positive active material electrode layer of one of the BPUs and the negative active material electrode layer of the other one of the BPUs for electrically isolating the current collectors of those two BPUs. The current collectors of any two adjacent BPUs, along with the active material electrode layers and electrolyte therebetween, may also be a sealed single cell or cell segment. A battery that includes a stack of such cells, each having a portion of a first BPU and a portion of a second BPU, shall be referred to herein as a “stacked bi-polar” battery.
While the positive side of a first BPU and the negative side of a second BPU may form a first cell, the positive side of the second BPU may likewise form a second cell with the negative side of a third BPU or the negative side of a negative MPU, for example. Therefore, an individual BPU may be included in two different cells of a stacked bi-polar battery. The series configuration of these cells in a stack may cause the voltage potential to be different between current collectors. However, if the current collectors of a particular cell contact each other or if the common electrolyte of the two BPUs in a first cell is shared with any other cell in the stack, the voltage and energy of the battery would fade (i.e., discharge) quickly to zero.
Conventional stacked bi-polar batteries use flat electrode plates. By using flat plates and isolating them by use of an edge seal, cells in a stacked electrochemical battery may operate substantially independently. As the independent cells are charged and discharged, slight pressure differences may develop between adjacent cells. If the pressure difference between the adjacent cells exceeds a few pounds per square inch, then the flat electrode may deflect from the first cell towards the second cell. This deflection may strain the separator material of the second cell, creating a “hot spot” where a short circuit may develop. Because the physical components and the chemistry of individual cells will generally be slightly different from one another, pressure differentials between cells will generally exist. Therefore, it is desirable to mitigate the pressure differential from one cell to the next. Accordingly, it would be desirable to provide a stacked bi-polar battery with reduced electrode plate deflection and improved pressure equalization.